Machine vision and electro-optical sensors are extremely useful for rapid accurate data gathering from objects, such as parts being manufactured. The ability of such sensors to be employed is however, limited by their ability to work in the manufacturing or other environment in question. While problems of EMI, liquids, etc. can generally be solved, the more severe environments cause degradation of the optical components of the sensor-particularly the front protective window.
There are two kinds of such contamination. The first are those contaminants with locally impact or react with the window to adversely alter its optical characteristics or eventually destroy it. The second are those which coat the window, seldom destroying it, but generally reducing optical performance over a larger window region.
An example of the former, which has been encountered by the inventors where optical sensors are used in car body and other fabricated parts assembly, is window contamination by weld splatter, or drips. During welding, particles of metal, the temperature of which depends on the process, are shot off, or fall onto the sensor window--melting, crazing, staining, or otherwise damaging it. The particular problem is damage to the front window of the sensor which protect the basic optics inside. These windows are typically assumed to be flat and clear, and departures from this condition due to contamination or damage, can change the characteristics of the sensor, or kill its operation completely, depending on the optical design.